Re: [dpdk-dev] [PATCH v2] lib/rte_rib6: fix stack buffer overflow

["Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>]

On 18/06/2021 19:22, Medvedkin, Vladimir wrote:
> Hi Owen,
> 
> Just a few nits inlined below
> 
> On 16/06/2021 21:18, ohilyard@iol.unh.edu wrote:
>> From: Owen Hilyard <ohilyard@iol.unh.edu>
>>
>> ASAN found a stack buffer overflow in lib/rib/rte_rib6.c:get_dir.
>> The fix for the stack buffer overflow was to make sure depth
>> was always < 128, since when depth = 128 it caused the index
>> into the ip address to be 16, which read off the end of the array.
>>
>> While trying to solve the buffer overflow, I noticed that a few
>> changes could be made to remove the for loop entirely.
>>
>> Fixes: f7e861e21c ("rib: support IPv6")
>>
>> Signed-off-by: Owen Hilyard <ohilyard@iol.unh.edu>
>> ---
>>   lib/rib/rte_rib6.c | 27 +++++++++++++++++++--------
>>   1 file changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/lib/rib/rte_rib6.c b/lib/rib/rte_rib6.c
>> index f6c55ee45..a4daf12ca 100644
>> --- a/lib/rib/rte_rib6.c
>> +++ b/lib/rib/rte_rib6.c
>> @@ -79,20 +79,31 @@ is_covered(const uint8_t 
>> ip1[RTE_RIB6_IPV6_ADDR_SIZE],
>>   static inline int
>>   get_dir(const uint8_t ip[RTE_RIB6_IPV6_ADDR_SIZE], uint8_t depth)
>>   {
>> -    int i = 0;
>> -    uint8_t p_depth, msk;
>> -
>> -    for (p_depth = depth; p_depth >= 8; p_depth -= 8)
>> -        i++;
>> -
>> -    msk = 1 << (7 - p_depth);
>> -    return (ip[i] & msk) != 0;
>> +    uint8_t index, msk;
>> +
>> +    /* depth & 127 clamps depth to values that will not
> 
> Please be consistent with the coding style. Check 1.3.1 in 
> https://doc.dpdk.org/guides/contributing/coding_style.html
> 
>> +     * read off the end of ip.
>> +     * depth is the number of bits deep into ip to traverse, and
>> +     * is incremented in blocks of 8 (1 byte). This means the last
>> +     * 3 bits are irrelevant to what the index of ip should be.
>> +     */
>> +    index = (depth & 127) >> 3;
> 
> (depth & INT8_MAX) / UINT8_MAX ?

Ugh...
sed 's/UINT8_MAX/CHAR_BIT'

> 
>> +
>> +    /*
>> +     * msk is the bitmask used to extract the bit used to decide the
>> +     * direction of the next step of the binary search.
>> +     */
>> +    msk = 1 << (7 - (depth & 7));
>> +
>> +    return (ip[index] & msk) != 0;
>>   }
>>   static inline struct rte_rib6_node *
>>   get_nxt_node(struct rte_rib6_node *node,
>>       const uint8_t ip[RTE_RIB6_IPV6_ADDR_SIZE])
>>   {
>> +    if (node->depth == 128)
>> +        return NULL;
> 
> please use RIB6_MAXDEPTH instead of 128.
> Also I'd put a blank line before the final return.
> 
>>       return (get_dir(ip, node->depth)) ? node->right : node->left;
>>   }
>>
> 
> while this is a bug fix, please add Cc: stable@dpdk.org on v3 to 
> backport this patch.
> 
> Apart from that LGTM.
> 

-- 
Regards,
Vladimir